The present disclosure relates to a power amplifier circuit. A mobile communication terminal such as a cellular phone includes a power amplifier circuit that amplifies a radio frequency (RF) signal to be transmitted to a base station. The power amplifier circuit includes a transistor that amplifies an RF signal, and a bias circuit that supplies a bias current to the transistor. For example, as described in Japanese Unexamined Patent Application Publication No. 2014-171170, a known power amplifier module includes, as a bias circuit of the type described above, an emitter follower transistor that supplies a bias current to the transistor, and a constant voltage generation circuit that generates a constant voltage to be supplied to the collector of the emitter follower transistor.
A known technique for improving the efficiency of a power amplifier circuit is envelope tracking (ET) control for controlling a power supply voltage in accordance with the level of an RF signal. In ET control, the value of a power supply voltage is controlled in accordance with the level of an RF signal to increase efficiency such as power-added efficiency (PAE). In this case, a larger change in gain (gain dispersion) relative to a change in a power supply voltage to be supplied to a transistor enables the use of a higher efficiency power supply voltage value while keeping gain flatness. In ET control, therefore, the greater the gain dispersion of a power amplifier circuit, the more preferable.